Hi there!
I am wondering if this ever got resolved, as I am having difficulty upgrading a saved world with mods from 1.6.4 to 1.7.10 (forge-1.7.10-10.13.2.1291-universal).
If I try to bring over my old world (that had previously run on minecraftforge-universal-1.6.4-9.11.1.1345), I get some pretty funky results, like air being replaced by Bibliocraft desk lamps, missing textures, crashes, etc... that's just an example, it's not always desk lamps.
Any help would be greatly appreciated. Thank you.